The present invention relates generally to high pressure fuel injection valves or injectors for internal combustion engines, and, more specifically, to an injection valve that is directly controllable by a position actuating material (such as, for example, a piezoelectric or magnetostrictive material) and which includes a passive hydraulic link.
Direct injection of a gaseous fuel into the combustion chamber of an internal combustion engine is desirable for several reasons. For example, direct injection allows charge stratification, eliminating throttling losses associated with homogeneous charge engines. Additionally, with direct injection late in the compression stroke, a high-compression ratio can be maintained, maintaining efficiency. Further, when the fuel that is directly injected comprises natural gas, propane, or hydrogen, the emissions of NOx and particulate matter (PM) are significantly reduced. The directly injected gaseous fuel can be ignited with a glow plug, with a spark plug, with pilot diesel fuel, or with any other energy source. The gaseous fuel should be injected at high pressure to overcome the combustion chamber pressure, which is high at the end of the compression stroke. Preferably, the injection pressure is high enough to promote good mixing between the injected fuel and the combustion chamber air.
Direct injection at high pressures presents several challenges. The use of high-pressure fuels for direct injection results in high fuel pressures existing within the injection valve or injector. As a result, when closed, the injection valve should typically be strongly seated to avoid leakage of the fuel into the combustion chamber between injection events. When the valve is a needle valve, the valve is seated when the sealing surfaces of the movable valve needle and the valve seat are in fluid-tight contact with each other. The valve seat is generally part of the valve housing or body. For an outward opening valve, such as a poppet valve, the valve is closed when a valve member is retracted within the valve body so that the sealing surfaces of the valve member are pressed against the valve seat to form a fluid-tight seal. A fuel injection valve with an xe2x80x9coutwardxe2x80x9d opening configuration is defined herein as an injection valve for an internal combustion engine which employs a valve member that is movable in the direction of the engine combustion chamber to an open position and in the opposite direction to a closed position. Terms used to describe such a valve member include, for example, pintle shaft, valve stem, and valve shaft. Outward opening injection valves typically comprise a circular valve head mounted transversely on the valve member for axial motion towards and away from a mating circular valve seat associated with the valve body.
Moreover, compared to low-pressure systems, higher forces are needed to open or close the injection valve. For example, for a needle valve that employs an inwardly opening valve needle, when the needle is in the open position it may be subjected to high forces from the pressurized fuel. Conversely, with an outward opening injection valve, a high amount of force is required to keep the valve closed against the high fuel pressure within the injection valve body.
Additionally, there is only a small window of time during which the fuel can be injected. For example, at 4500 revolutions per minute (RPM), at full load, all of the fuel is preferably injected in less than 2-3 milliseconds.
Nearly all known direct fuel injection systems in internal combustion engines have been hydraulically actuated. These systems rely on a hydraulic fluid to provide the force that is needed to open an injection valve (or valves, when the engine comprises a plurality of combustion chambers). Accordingly, at typical engine operating speeds, hydraulically actuated injectors rely on rapid changes in the hydraulic fluid pressure to open and close the injection valve(s). An injection valve is typically opened by increasing the hydraulic fluid pressure and closed by reducing the hydraulic fluid pressure, such that the opening force applied to the injection valve is reduced, causing the valve to close. However, in the context of a conventional gaseous injection valve, hydraulic operation presents several drawbacks, including:
the need for additional hydraulic hardware such as a hydraulic pump, valves, and a reservoir for the hydraulic fluid;
the need for a seal to be established between the variable pressure hydraulic fluid and the high pressure gaseous fuel;
increased bulkiness of the injection valve assembly because of the additional hardware requirements; and
delayed response of the system caused by time delays associated with the dynamic flow of the hydraulic fluid, the actuation of the electronic hydraulic valve hardware and the movement of the needle that controls gas flow from the injection valve.
Moreover, the degree of controllability of the movement of the injection valve is low when the motive force is provided by a pressurized fluid rather than by a directly controllable source. In this respect, it is difficult to control lift, resulting in limited lift control capabilities when using hydraulically actuated injection valve with a double-spring configuration. Therefore, it is desirable to avoid the use of hydraulics to operate gaseous fuel injectors, particularly for high-speed engines. xe2x80x9cLiftxe2x80x9d in the context of injection valves is defined herein as the displacement of the valve needle or member away from its closed/seated position to its open position.
U.S. Pat. No. 5,779,149 describes an injector using a piezoelectric actuator acting on a hydraulic control valve through the intermediate of a hydraulic amplifier, which serves to amplify the movement of the actuator. The hydraulic control valve allows the main injection valve to open and close to meter the amount of fuel injected.
A problem with employing a piezoelectric or magnetostrictive actuator to operate a control valve, which in turn controls the flow of a hydraulic fluid to operate an injection valve, is that this arrangement requires the intermediate action of a hydraulic fluid. Any delays caused by the displacement of the hydraulic fluid causes delays in the actuation of the injector. Accordingly, there is a need for an injector that is directly actuated by an actuator without an intermediate active hydraulic operator generating any actuating forces. Another disadvantage of active hydraulically operated systems is that a hydraulic fluid needs to be supplied and drained from a hydraulic cylinder. When diesel fuel is the main fuel used by the engine, the diesel fuel may be used as the hydraulic fluid. However, when a gaseous fuel is the engine""s main fuel, a separate hydraulic fluid system is needed to operate injectors that rely on hydraulic actuation.
An injection valve injects fuel into a combustion chamber of an internal combustion engine. The injection valve comprises:
(a) a valve housing comprising:
a fuel inlet port;
an interior chamber fluidly connected to the fuel inlet port; and
a valve seat for cooperating with a valve member to seal the interior chamber from the combustion chamber when the injection valve is closed;
(b) the valve member having one end disposed within the valve housing and an opposite end extendable from the valve seat toward the combustion chamber, wherein the valve member comprises a sealing surface that fluidly seals against the valve seat when the injection valve is closed and that is liftable away from the valve seat when the injection valve is open, wherein valve lift equals the distance traveled by the sealing surface away from the valve seat;
(c) a biasing mechanism associated with the valve member, the biasing mechanism applying a closing force to the valve member when the valve member is in the closed position;
(d) an actuator assembly associated with the valve member, wherein the actuator assembly may be actuated to apply an opening force to the valve member stronger than the closing force, for moving the valve member to the open position; and
(e) a hydraulic link assembly comprising a passive hydraulic link having a hydraulic fluid thickness through which the opening and closing forces are transmitted, whereby the hydraulic fluid acts substantially as a solid with the thickness being substantially constant while the actuator assembly is actuated and wherein the thickness of the hydraulic link is adjustable while the actuator assembly is not actuated in response to changes in the dimensional relationship between components of the injection valve to maintain a desired valve lift upon actuation of the actuator assembly.
In a preferred embodiment, the thickness of the hydraulic link is auto-adjustable in response to changes in the dimensional relationship caused by differential thermal expansion, and/or wear to components of the injection valve. The hydraulic link assembly preferably comprises a fluidly sealed hydraulic cylinder that is fluidly sealed from the interior chamber. The hydraulic link assembly comprises a piston and hydraulic fluid disposed within the hydraulic cylinder. The hydraulic fluid is preferably a liquid such as, for example motor oil or grease. The piston may be an integral part of the valve member.
In a preferred injection valve the actuator assembly comprises a dimensionally responsive member. The dimensionally responsive member can be formed from a magnetostrictive material. The preferred magnetostrictive material comprises a metal alloy comprising terbium, dysprosium and iron. The preferred actuator assembly further comprises an electric coil disposed in an annular space around the dimensionally responsive member and a flux tube disposed in an annular space around the electric coil. The actuator assembly is preferably disposed within the interior chamber. The dimensionally responsive member can also be formed from a piezoelectric material. A preferred injection valve further comprises a compression spring member for applying a compressive force to the dimensionally responsive member.
In one embodiment, the fuel inlet is positioned so that fuel enters the valve housing and passes through the actuator and hydraulic link assemblies in the interior chamber. In this embodiment, the flow of fuel over these assemblies helps to remove heat generated by the activation of the actuator and reduces the effect of differential temperatures within the injection valve. In another embodiment, the fuel inlet is positioned near the valve tip so that the fuel flowing through the injection valve does not come into contact with the actuator assembly. This embodiment simplifies the construction of the actuator and hydraulic link assemblies since there is no need to provide fluid passages for the fuel to flow to the valve tip.
In a preferred injection valve, the lift is controllable by varying at least one of the electric current, the electric voltage and the magnetic field imposed upon the dimensionally responsive member. The valve member is preferably controllable such that the valve member moves between the open and closed positions in less than about 200 microseconds.
The injection valve preferably further comprises a biasing mechanism for applying a compressive force to the dimensionally responsive member. The biasing mechanism preferably comprises a spring. The spring preferably comprises at least one disc spring.
In a preferred injection valve, the fuel is gaseous and the hydraulic fluid is a liquid. The preferred hydraulic fluid is a liquid selected from the group consisting of motor oil and grease.
The present injection valve is particularly suited for injecting a gaseous fuel because the ability to modulate the movement of the valve member may be beneficially used to slow down the closing action of the valve member to reduce impact upon closing. When a liquid fuel is injected, the closing impact is dampened by the displacement of the thin liquid fuel layer, which is considerably denser than gaseous fuels. When the fuel is a gaseous fuel, it can be injected into the combustion chamber at a pressure greater than about 2000 psi (about 13.8 MPa).
While the hydraulic link in the present injection valve is designed to compensate for changes in the dimensional relationships between valve components, including changes caused by differential thermal expansion, the demands placed upon the hydraulic link may be reduced by the selection of materials for the valve components that have similar thermal expansion coefficients. In this regard, the valve housing, valve member and actuator assembly are preferably selected from materials having thermal expansion coefficients sufficiently compatible such that changes in the dimensional relationship between the components caused by changes in temperature are reduced.
A magnetostrictive material that is suitable for use in the present injection valve comprises a material known as ETREMA Terfenol-D(copyright) magnetostrictive alloy that is available from Etrema Products Inc. ETREMA Terfenol-D(copyright) magnetostrictive alloy is a metal alloy composed of terbium, dysprosium and iron.
In a preferred embodiment, the valve member, actuated by an actuator assembly that includes a dimensionally responsive member, is controllable to move between the closed and open positions in less than about 200 microseconds.
To improve the range of valve lift for a given length of the dimensionally responsive member, a compressive force may be applied to the dimensionally responsive member. By pre-loading the dimensionally responsive member, net displacement may be increased per respective unit of applied magnetic field (in the case of a dimensionally responsive member formed of magnetostrictive material) or applied voltage (in the case of a dimensionally responsive member formed of piezoelectric material). Accordingly, a biasing mechanism may be employed for applying a compressive force to pre-load the dimensionally responsive member. The biasing member preferably comprises at least one spring, most preferably at least one disc spring (also known as a Belleville spring or Belleville washer).
The injection valve housing may comprise a plurality of parts that are joined with each other to provide a fluidly sealed body. For example, the valve housing may comprise a hollow main housing with a removable valve cap that allows access to the valve components disposed within the main housing. The valve housing may further comprise a separate valve tip so that it is replaceable when worn. In addition, the valve tip may be designed so that it is the only portion of the valve body that is directly exposed to the interior of the combustion chamber. In this case the valve tip may be made from a material that will provide greater durability when directly exposed to the conditions that might be expected within a combustion chamber.
A preferred fuel injection valve for injecting fuel into a combustion chamber of an internal combustion engine comprises:
(a) a valve housing comprising:
a fuel inlet port;
an interior chamber fluidly connected to the fuel inlet port;
a valve seat provided on an end of the housing that faces the combustion chamber;
(b) a valve member comprising a shaft portion having a first end to which a circular head is transversely mounted wherein the head provides an annular sealing surface that faces the valve seat, and a second end of the shaft is associated with a piston portion, the valve member movable between a closed position at which the sealing surface contacts the valve seat to fluidly seal the interior chamber from the combustion chamber, and an open position at which the sealing surface is spaced apart from the valve seat whereby the interior chamber is fluidly connected with combustion chamber, wherein valve lift equals distance traveled by the sealing surface away from the valve seat;
(c) a biasing mechanism associated with the piston portion of the valve member, the biasing mechanism applying a closing force to the valve member when the valve member is in the closed position;
(d) an actuator assembly for applying an opening force to the valve member that is stronger than the closing force, for moving the valve member to the open position, the actuator assembly comprising a member having dimensional responsiveness to the imposition of at least one of an electric current, an electric voltage and a magnetic field, the dimensionally responsive member disposed between a fixed pole maintained in a fixed position relative to the valve housing and a sliding pole, the sliding pole being displaceable by expansion of the dimensionally responsive member; and
(e) a hydraulic link assembly comprising a fluidly sealed hydraulic cylinder disposed about the piston portion of the valve member, a hydraulic fluid disposed within the hydraulic cylinder, wherein the opening and closing forces applied to the valve member are transmitted through a thickness of the hydraulic fluid whereby the hydraulic fluid acts as a hydraulic link and the thickness is automatically adjustable in response to changes in the dimensional relationship between components of the injection valve to maintain a desired valve lift upon actuation of the actuator assembly.
A method of using a shaped waveform to control electric current to actuate an injection valve for an internal combustion engine employs a dimensionally responsive actuator assembly comprising at least one of a magnetostrictive and a piezoelectric material, and a controller to govern valve lift and duration according to values predetermined for engine load demands within the operating range of the engine by the controller controlling current and voltage directed to the actuator assembly. The method comprises, for each injection event:
(a) initiating an injection event by rapidly increasing current to a magnitude that is known to correspond to a desired lift by applying high frequency voltage cycles and in each cycle maintaining a net positive voltage;
(b) maintaining a current to control the desired lift for a duration predetermined by the controller; and
(c) concluding an injection event by decreasing current until it is reduced to zero amps by applying high frequency voltage cycles and in each cycle maintaining a net negative voltage.
In a preferred shaped waveform method, the step of initiating an injection event further comprises initially increasing current to a spike value higher than the value for the desired lift to rapidly open the valve and then reducing current to the value to cause the desired lift. The spike value is preferably up to about an order of magnitude higher than the value needed to cause the desired lift. The preferred method further comprises applying high frequency voltage cycles between offsetting positive and negative voltages to generate a current of close to zero amps immediately prior to an injection event. The time to open the valve from a closed position to the desired lift is less than about 175 microseconds, more preferably less than about 100 microseconds. More typically, however, the time needed to move the valve member between the closed position and the desired open position may be as short as about 250 microseconds.
A method of operating a fuel injection valve for an internal combustion engine, in which the injection valve has a longitudinal axis, comprises:
(a) actuating a dimensionally responsive member comprising at least one of a magnetostrictive material and a piezoelectric material, the dimensionally responsive member expanding in length in the direction of the longitudinal axis upon actuation of the actuator;
(b) transferring movement caused by the actuated dimensionally responsive member through a passive hydraulic link to cause a corresponding movement of a valve member to open the valve by lifting the valve member away from a valve seat and compressing a biasing mechanism that biases the valve in a closed position, the passive hydraulic link comprising a hydraulic cylinder which houses a piston and is filled with a hydraulic fluid, wherein the hydraulic fluid forms a layer between the piston and a cylinder head and because of the short duration that the valve is open, the hydraulic fluid does not have time to flow from one side of the piston to the other side and while the injection valve is open, the layer of hydraulic fluid acts as an incompressible solid so that movement caused by the actuation of the dimensionally responsive member is transmitted through the fluid layer;
(c) deactuating the dimensionally responsive member to contract the length of the dimensionally responsive member to unload the biasing mechanism and cause a corresponding movement of the valve member to close the valve;
(d) providing sufficient time between consecutive valve openings to allow at least some of the hydraulic fluid within the passive hydraulic link to flow from one side of the piston to the other side of the piston.
An advantage of the present injection valve is that it may be employed for late-cycle high-pressure direct injection of fuels into internal combustion engines. For example, the present injection valve may be used to inject a gaseous fuel into the combustion chamber of an internal combustion engine at pressures of between about 2000 and 5000 psi (about 13.8 and 34.5 MPa). The present injection valve may be employed to introduce liquid fuels into internal combustion engines at even higher pressures.
Still another advantage of the present injection valve is that it provides an injection valve that eliminates the need for an active hydraulic operator and the associated high-pressure hydraulic system for generating the actuation force to actuate the injection valve. Conventional active hydraulic operators are different from the hydraulic link of the present invention, which may be described as a passive hydraulic link because the hydraulic fluid sealed within the hydraulic link assembly merely transmits the actuating forces but is not employed to generate an actuating force for actuating the valve. Rather, the purpose of the hydraulic link is to provide a load path for the opposing actuating forces that originate from at least one spring member and the actuator assembly. A benefit of eliminating the need for a conventional active hydraulic operator is the elimination of the associated active hydraulic systems. Conventional active hydraulic actuators, such as those that employ rapidly increasing and decreasing hydraulic fluid pressure to actuate an injection valve, are connected to a source of high pressure hydraulic fluid and have valves for controlling the flow of hydraulic fluid in and out of the active hydraulic operator. Active hydraulic actuators employ hydraulic fluid that is moved in and out of a hydraulic cylinder and when the hydraulic cylinder is fluidly connected to a source of high pressure hydraulic fluid, the high pressure hydraulic fluid that flows into the hydraulic cylinder generates the actuating force that is used to move the valve member. The actuating force is removed when the hydraulic cylinder is disconnected from the source of high-pressure hydraulic fluid and the hydraulic fluid is drained from the hydraulic cylinder. A disadvantage of active hydraulic actuators of this type is that there is a lag time associated with moving the hydraulic fluid into and out of the hydraulic cylinder.
A further advantage of the passive hydraulic link is that it may be employed to correct for differential thermal expansion, wear and dimensional variability within permitted manufacturing and assembly tolerances. The disclosed passive hydraulic link accomplishes this by auto-adjusting itself in response to these effects by allowing movement of hydraulic fluid between opposite sides of the hydraulic piston. The actuator assembly thus re-zeroes itself to ensure that the desired valve member lift is maintained.
An advantage of employing a directly actuated injection valve is that a shaped control pulse may be employed to control the acceleration and deceleration of the valve member as it moves between the open and closed positions. For example, when a magnetostrictive actuator is employed, the current applied to the electromagnetic coil can be controlled, for example, to reduce the current in a manner that will close the valve gently. Similarly, when a piezoelectric actuator is employed, the voltage applied to the piezoelectric stack can be controlled, for example, to accelerate the opening of the valve by initially providing an over-voltage (that is, a voltage that is higher than the voltage that is needed to provide the necessary displacement). Thus, control pulses may be employed to control the expansion and contraction of magnetostrictive or piezoelectric actuators to control the movement of the valve member. An advantage of controlling the deceleration of the valve member is that the impact of the valve member on the valve seat upon closing can be reduced to reduce the wear on the valve components, thereby improving durability.
Yet another advantage of the present injection valve is that the control pulse may be shaped to provide for partial lifting of the valve member in a repeatable manner. The amount of lift may be controlled by shaping the control pulse to control the amount of electric current or voltage directed to the respective magnetostrictive or piezoelectric actuator assembly.
Still another advantage of the disclosed injection valve is that the actual valve lift is very small (typically much less than 0.1 millimeter), so that compared to valves designed for greater valve lift, to fully open or close the valve, the valve member velocity can be lower resulting in less impact and wear.
These and other advantages are provided by a directly actuated injector as described below.